The term glaucoma describes a specific pattern of optic nerve head and visual field damage caused by a number of different diseases of the eye, most (but not all) of which are associated with an elevated eye pressure. Glaucoma is currently considered to be a progressive neurodegenerative disorder. Low-pressure glaucoma (LPG) is a type of open-angle glaucoma (OAG) with progressive visual field and optic nerve damage despite an untreated eye pressure in the statistically normal (mean 15.9, SD 2.9 mmHg) range, usually less than 21 mmHg. Therefore, in this condition, pressure-independent mechanisms (e.g., vascular or structural defects of the optic nerve) may be the main, if not the sole, cause of the optic neuropathy. LPG represents 6.7% to 68.3% of all OAGs.